Power parameters for ultrasonic catheter

ABSTRACT

In one embodiment of the present invention, a method of applying ultrasonic energy to a treatment site within a patient&#39;s vasculature comprises positioning an ultrasound radiating member at a treatment site within a patient&#39;s vasculature. The method further comprises activating the ultrasound radiating member to produce pulses of ultrasonic energy at a cycle period T≦1 second. The acoustic parameters such as peak power, pulse width, pulse repetition frequency and frequency or any combination of them can be varied non-linearly.

PRIORITY INFORMATION

This application claims the priority benefit of U.S. ProvisionalApplication No. 60/884,010 filed Jan. 8, 2007 and U.S. ProvisionalApplication No. 60/969,524 filed Aug. 31, 2007, the entire contents ofwhich are hereby incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates generally to ultrasound systems, and morespecifically to ultrasound catheter systems.

BACKGROUND OF THE INVENTION

Ultrasonic energy had been used to enhance the intravascular deliveryand/or effect of various therapeutic compounds. In one system,ultrasound catheters are used to deliver ultrasonic energy andtherapeutic compounds to a treatment site within a patient'svasculature. Such ultrasound catheters can comprise an elongate memberconfigured to be advanced through a patient's vasculature and anultrasound assembly that is positioned near a distal end portion of theelongate member. The ultrasound assembly is configured to emitultrasonic energy. Such ultrasound catheters can include a fluiddelivery lumen that is used to deliver the therapeutic compound to thetreatment site. In this manner, ultrasonic energy is delivered to thetreatment site to enhance the effect and/or delivery of the therapeuticcompound.

For example, ultrasound catheters have been successfully used to treathuman blood vessels that have become occluded by plaque, thrombi, embolior other substances that reduce the blood carrying capacity of thevessel. See, for example, U.S. Pat. No. 6,001,069. To remove theocclusion, the ultrasound catheter is advanced through the patient'svasculature to deliver a therapeutic compound containing dissolutioncompounds directly to the occlusion. To enhance the effect and/ordelivery of the therapeutic compound, ultrasonic energy is emitted intothe therapeutic compound and/or the surrounding tissue at the treatmentsite. In other applications, ultrasound catheters are used for otherpurposes, such as for the delivery and activation of light activateddrugs. See, for example, U.S. Pat. No. 6,176,842.

SUMMARY OF THE INVENTION

While such ultrasound catheters systems have been proven to besuccessful, there is a general need to continue to improve theeffectiveness and speed of such systems. In this manner, treatmentand/or hospital time can be reduced.

Accordingly, one aspect of the present invention comprises an ultrasoundcatheter system comprising a catheter having at least ultrasonicelement; a control system configured to generate power parameters todrive the ultrasonic element to generate ultrasonic energy. The controlsystem is configured to vary non-linearly at least one of the powerparameters.

Another aspect of the present invention comprises a method of operatingan ultrasonic catheter. In the method, a catheter with at least oneultrasonic element is advanced to a treatment site in a patient'svascular system. The at least one ultrasonic element is driven togenerate ultrasonic energy. A therapeutic compound is delivered to thetreatment site through the catheter. The driving parameters of theultrasonic element are non-linearly varied to attain non-linear acousticoutput.

Another aspect of the present invention is a control system for anultrasound catheter. The control system includes control unit configuredto non-linearly vary acoustic parameters of an ultrasonic element of anultrasonic catheter.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the cavitation promoting systems and methodsdisclosed herein are illustrated in the accompanying drawings, which arefor illustrative purposes only. The drawings comprise the followingfigures, in which like numerals indicate like parts.

FIG. 1 is a schematic illustration of certain features of an exampleultrasonic catheter.

FIG. 2 is a cross-sectional view of the ultrasonic catheter of FIG. 1taken along line 2-2.

FIG. 3 is a schematic illustration of an elongate inner core configuredto be positioned within the central lumen of the catheter illustrated inFIG. 2.

FIG. 4 is a cross-sectional view of the elongate inner core of FIG. 3taken along line 4-4.

FIG. 5 is a schematic wiring diagram illustrating a preferred techniquefor electrically connecting five groups of ultrasound radiating membersto form an ultrasound assembly.

FIG. 6 is a schematic wiring diagram illustrating a preferred techniquefor electrically connecting one of the groups of FIG. 5.

FIG. 7A is a schematic illustration of the ultrasound assembly of FIG. 5housed within the inner core of FIG. 4.

FIG. 7B is a cross-sectional view of the ultrasound assembly of FIG. 7Ataken along line 7B-7B.

FIG. 7C is a cross-sectional view of the ultrasound assembly of FIG. 7Ataken along line 7C-7C.

FIG. 7D is a side view of an ultrasound assembly center wire twistedinto a helical configuration.

FIG. 8 illustrates the energy delivery section of the inner core of FIG.4 positioned within the energy delivery section of the tubular body ofFIG. 2.

FIG. 9 illustrates a wiring diagram for connecting a plurality oftemperature sensors with a common wire.

FIG. 10 is a block diagram of a feedback control system for use with anultrasonic catheter.

FIG. 11 is a longitudinal cross-sectional view of selected components ofan exemplary ultrasound catheter assembly that is particularlywell-suited for treatment of cerebral vascular occlusions, and thatincludes a cavitation promoting surface.

FIG. 12 schematically illustrates an example ultrasonic energy pulseprofile.

FIG. 13 is a chart showing the lysis enhancement factor of a variety ofultrasonic protocols.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As used herein, the term “ultrasonic energy” is used broadly, includesits ordinary meaning, and further includes mechanical energy transferredthrough pressure or compression waves with a frequency greater thanabout 20 kHz. Ultrasonic energy waves have a frequency between about 500kHz and about 20 MHz in one example embodiment, between about 1 MHz andabout 3 MHz in another example embodiment, of about 3 MHz in anotherexample embodiment, and of about 2 MHz in another example embodiment. Asused herein, the term “catheter” is used broadly, includes its ordinarymeaning, and further includes an elongate flexible tube configured to beinserted into the body of a patient, such as into a body part, cavity,duct or vessel. As used herein, the term “therapeutic compound” is usedbroadly, includes its ordinary meaning, and encompasses drugs,medicaments, dissolution compounds, genetic materials, and othersubstances capable of effecting physiological functions. A mixturecomprising such substances is encompassed within this definition of“therapeutic compound”. As used herein, the term “end” is used broadly,includes its ordinary meaning, and further encompasses a regiongenerally, such that “proximal end” includes “proximal region”, and“distal end” includes “distal region”.

As expounded herein, ultrasonic energy is often used to enhance thedelivery and/or effect of a therapeutic compound. For example, in thecontext of treating vascular occlusions, ultrasonic energy has beenshown to increase enzyme mediated thrombolysis by enhancing the deliveryof thrombolytic agents into a thrombus, where such agents lyse thethrombus by degrading the fibrin that forms the thrombus. Thethrombolytic activity of the agent is enhanced in the presence ofultrasonic energy in the thrombus. However, it should be appreciatedthat the invention should not be limited to the mechanism by which theultrasound enhances treatment unless otherwise stated. In otherapplications, ultrasonic energy has also been shown to enhancetransfection of gene-based drugs into cells, and augment transfer ofchemotherapeutic drugs into tumor cells. Ultrasonic energy deliveredfrom within a patient's body has been found to be capable of producingnon-thermal effects that increase biological tissue permeability totherapeutic compounds by up to or greater than an order of magnitude.

Use of an ultrasound catheter to deliver ultrasonic energy and atherapeutic compound directly to the treatment site mediates orovercomes many of the disadvantages associated with systemic drugdelivery, such as low efficiency, high therapeutic compound use rates,and significant side effects caused by high doses. Local therapeuticcompound delivery has been found to be particularly advantageous in thecontext of thrombolytic therapy, chemotherapy, radiation therapy, andgene therapy, as well as in applications calling for the delivery ofproteins and/or therapeutic humanized antibodies. However, it should beappreciated that in certain arrangements the ultrasound catheter canalso be used in combination with systemic drug delivery instead or inaddition to local drug deliver. In addition, local drug delivery can beaccomplished through the use of a separate device (e.g., catheter).

As will be described below, the ultrasound catheter can include one ormore one or more ultrasound radiating members positioned therein. Suchultrasound radiating members can comprise a transducer (e.g., a PZTtransducer), which is configured to convert electrically energy intoultrasonic energy. In such embodiments, the PZT transducer is excited byspecific electrical parameters (herein “power parameters” that cause itto vibrate in a way that generates ultrasonic energy). As will beexplained below, Applicants have discovered that by non-linearly (e.g.,randomly or pseudo randomly) varying one or more of the power parametersthe effectiveness of the ultrasound catheter (e.g., the effectiveness ofenhancing the removal of a thrombus) can be significantly enhanced.While, for example, U.S. Pat. No. 5,720,710 taught that randomlychanging the frequency of the ultrasonic frequency could significantlyenhance the remedial effect of the ultrasonic energy, these results withrespect to varying the other acoustic parameters were not expected. Inaddition, because PZT transducers are often configured to be driven aparticularly frequency, varying the other acoustic parameters may havesignificant advantages over varying the frequency. In addition, varyingthe electrical parameters may also be used in combination with varyingthe frequency (e.g., in a manner taught by U.S. Pat. No. 5,720,710.

The techniques disclosed herein are compatible with a wide variety ofultrasound catheters, several examples of which are disclosed in USAPatent Application Publication US 2004/0024347 A1 (published 5 Feb.2004; discloses catheters especially well-suited for use in theperipheral vasculature) and USA Patent Application Publication2005/0215942 A1 (published 29 Sep. 2005; discloses catheters especiallywell-suited for use in the cerebral vasculature). Certain of thetechniques disclosed herein are compatible with ultrasound cathetersthat would be unable to generate cavitation at an intravasculartreatment site but for the use of such techniques.

With reference to the illustrated embodiments, FIG. 1 illustrates anultrasonic catheter 10 configured for use in a patient's vasculature.For example, in certain applications the ultrasonic catheter 10 is usedto treat long segment peripheral arterial occlusions, such as those inthe vascular system of the leg, while in other applications theultrasonic catheter 10 is used to treat occlusions in the small vesselsof the neurovasculature or other portions of the body (e.g., otherdistal portions of the vascular system). Thus, the dimensions of thecatheter 10 are adjusted based on the particular application for whichthe catheter 10 is to be used.

The ultrasonic catheter 10 generally comprises a multi-component,elongate flexible tubular body 12 having a proximal region 14 and adistal region 15. The tubular body 12 includes a flexible energydelivery section 18 located in the distal region 15 of the catheter 10.The tubular body 12 and other components of the catheter 10 aremanufactured in accordance with a variety of techniques. Suitablematerials and dimensions are selected based on the natural andanatomical dimensions of the treatment site and on the desiredpercutaneous access site.

For example, in a preferred embodiment the proximal region 14 of thetubular body 12 comprises a material that has sufficient flexibility,kink resistance, rigidity and structural support to push the energydelivery section 1800 through the patient's vasculature to a treatmentsite. Examples of such materials include, but are not limited to,extruded polytetrafluoroethylene (“PTFE”), polyethylenes (“PE”),polyamides and other similar materials. In certain embodiments, theproximal region 14 of the tubular body 12 is reinforced by braiding,mesh or other constructions to provide increased kink resistance andpushability. For example, in certain embodiments nickel titanium orstainless steel wires are placed along or incorporated into the tubularbody 12 to reduce kinking.

The energy delivery section 18 of the tubular body 1200 optionallycomprises a material that (a) is thinner than the material comprisingthe proximal region 1400 of the tubular body 1200, or (b) has a greateracoustic transparency than the material comprising the proximal region14 of the tubular body 12. Thinner materials generally have greateracoustic transparency than thicker materials. Suitable materials for theenergy delivery section 1800 include, but are not limited to, high orlow density polyethylenes, urethanes, nylons, and the like. In certainmodified embodiments, the energy delivery section 18 is formed from thesame material or a material of the same thickness as the proximal region18.

One or more fluid delivery lumens are incorporated into the tubular body12. For example, in one embodiment a central lumen passes through thetubular body 12. The central lumen extends through the length of thetubular body 1200, and is coupled to a distal exit port 1290 and aproximal access port 1310. The proximal access port 1310 forms part ofthe backend hub 1330, which is attached to the proximal region 14 of thecatheter 10. The backend hub 1330 optionally further comprises coolingfluid fitting 1460, which is hydraulically connected to a lumen withinthe tubular body 12. The backend hub 1330 also optionally comprises atherapeutic compound inlet port 1320, which is hydraulically connectedto a lumen within the tubular body 12. The therapeutic compound inletport 1320 is optionally also hydraulically coupled to a source oftherapeutic compound via a hub such as a Luer fitting.

The catheter 100 is configured to have one or more ultrasound radiatingmembers positioned therein. For example, in certain embodiments anultrasound radiating member is fixed within the energy delivery section18 of the tubular body, while in other embodiments a plurality ofultrasound radiating members are fixed to an assembly that is passedinto the central lumen. In either case, the one or more ultrasoundradiating members are electrically coupled to a control system 1100 viacable 1450. In one embodiment, the outer surface of the energy delivery18 section can include an cavitation promoting surface configured toenhance/promote cavitation at the treatment site.

With reference to FIG. 2-10, an exemplary arrangement of the energydelivery section 18 and other portions of the catheter 10 describedabove. This arrangement is particularly well-suited for treatment ofperipheral vascular occlusions.

FIG. 2 illustrates a cross section of the tubular body 12 taken alongline 2-2 in FIG. 1. In the embodiment illustrated in FIG. 2, three fluiddelivery lumens 30 are incorporated into the tubular body 12. In otherembodiments, more or fewer fluid delivery lumens can be incorporatedinto the tubular body 12. The arrangement of the fluid delivery lumens30 preferably provides a hollow central lumen 51 passing through thetubular body 12. The cross-section of the tubular body 12, asillustrated in FIG. 2, is preferably substantially constant along thelength of the catheter 10. Thus, in such embodiments, substantially thesame cross-section is present in both the proximal region 14 and thedistal region 15 of the catheter 10, including the energy deliverysection 18.

In certain embodiments, the central lumen 51 has a minimum diametergreater than about 0.030 inches. In another embodiment, the centrallumen 51 has a minimum diameter greater than about 0.037 inches. In onepreferred embodiment, the fluid delivery lumens 30 have dimensions ofabout 0.026 inches wide by about 0.0075 inches high, although otherdimensions may be used in other applications.

As described above, the central lumen 51 preferably extends through thelength of the tubular body 12. As illustrated in FIG. 1, the centrallumen 51 preferably has a distal exit port 29 and a proximal access port31. The proximal access port 31 forms part of the backend hub 33, whichis attached to the proximal region 14 of the catheter 10. The backendhub preferably further comprises cooling fluid fitting 46, which ishydraulically connected to the central lumen 51. The backend hub 33 alsopreferably comprises a therapeutic compound inlet port 32, which is inhydraulic connection with the fluid delivery lumens 30, and which can behydraulically coupled to a source of therapeutic compound via a hub suchas a Luer fitting.

The central lumen 51 is configured to receive an elongate inner core 34of which a preferred embodiment is illustrated in FIG. 3. The elongateinner core 34 preferably comprises a proximal region 36 and a distalregion 38. Proximal hub 37 is fitted on the inner core 34 at one end ofthe proximal region 36. One or more ultrasound radiating members arepositioned within an inner core energy delivery section 41 locatedwithin the distal region 38. The ultrasound radiating members 40 form anultrasound assembly 42, which will be described in detail below.

As shown in the cross-section illustrated in FIG. 4, which is takenalong lines 4-4 in FIG. 3, the inner core 34 preferably has acylindrical shape, with an outer diameter that permits the inner core 34to be inserted into the central lumen 51 of the tubular body 12 via theproximal access port 31. Suitable outer diameters of the inner core 34include, but are not limited to, about 0.010 inches to about 0.100inches. In another embodiment, the outer diameter of the inner core 34is between about 0.020 inches and about 0.080 inches. In yet anotherembodiment, the inner core 34 has an outer diameter of about 0.035inches.

Still referring to FIG. 4, the inner core 34 preferably comprises acylindrical outer body 35 that houses the ultrasound assembly 42. Theultrasound assembly 42 comprises wiring and ultrasound radiatingmembers, described in greater detail in FIGS. 5 through 7D, such thatthe ultrasound assembly 42 is capable of radiating ultrasonic energyfrom the energy delivery section 41 of the inner core 34. The ultrasoundassembly 42 is electrically connected to the backend hub 33, where theinner core 34 can be connected to a control system 100 via cable 45(illustrated in FIG. 1). Preferably, an electrically insulating pottingmaterial 43 fills the inner core 34, surrounding the ultrasound assembly42, thus preventing movement of the ultrasound assembly 42 with respectto the outer body 35. In one embodiment, the thickness of the outer body35 is between about 0.0002 inches and 0.010 inches. In anotherembodiment, the thickness of the outer body 35 is between about 0.0002inches and 0.005 inches. In yet another embodiment, the thickness of theouter body 35 is about 0.0005 inches.

In a preferred embodiment, the ultrasound assembly 42 comprises aplurality of ultrasound radiating members 40 that are divided into oneor more groups. For example, FIGS. 5 and 6 are schematic wiring diagramsillustrating one technique for connecting five groups of ultrasoundradiating members 40 to form the ultrasound assembly 42. As illustratedin FIG. 5, the ultrasound assembly 42 comprises five groups G1, G2, G3,G4, G5 of ultrasound radiating members 40 that are electricallyconnected to each other. The five groups are also electrically connectedto the control system 100.

As used herein, the terms “ultrasonic energy”, “ultrasound” and“ultrasonic” are broad terms, having their ordinary meanings, andfurther refer to, without limitation, mechanical energy transferredthrough longitudinal pressure or compression waves. Ultrasonic energycan be emitted as continuous or pulsed waves, depending on therequirements of a particular application. Additionally, ultrasonicenergy can be emitted in waveforms having various shapes, such assinusoidal waves, triangle waves, square waves, or other wave forms.Ultrasonic energy includes sound waves. In certain embodiments, theultrasonic energy has a frequency between about 20 kHz and about 20 MHz.For example, in one embodiment, the waves have a frequency between about500 kHz and about 20 MHz. In another embodiment, the waves have afrequency between about 1 MHz and about 3 MHz. In yet anotherembodiment, the waves have a frequency of about 2 MHz. The averageacoustic power is between about 0.01 watts and 300 watts. In oneembodiment, the average acoustic power is about 15 watts.

As used herein, the term “ultrasound radiating member” refers to anyapparatus capable of producing ultrasonic energy. For example, in oneembodiment, an ultrasound radiating member comprises an ultrasonictransducer, which converts electrical energy into ultrasonic energy. Asuitable example of an ultrasonic transducer for generating ultrasonicenergy from electrical energy includes, but is not limited to,piezoelectric ceramic oscillators. Piezoelectric ceramics typicallycomprise a crystalline material, such as quartz, that change shape whenan electrical current is applied to the material. This change in shape,made oscillatory by an oscillating driving signal, creates ultrasonicsound waves. In other embodiments, ultrasonic energy can be generated byan ultrasonic transducer that is remote from the ultrasound radiatingmember, and the ultrasonic energy can be transmitted, via, for example,a wire that is coupled to the ultrasound radiating member.

Still referring to FIG. 5, the control circuitry 100 preferablycomprises, among other things, a voltage source 102. The voltage source102 comprises a positive terminal 104 and a negative terminal 106. Thenegative terminal 106 is connected to common wire 108, which connectsthe five groups G1-G5 of ultrasound radiating members 40 in series. Thepositive terminal 104 is connected to a plurality of lead wires 110,which each connect to one of the five groups G1-G5 of ultrasoundradiating members 40. Thus, under this configuration, each of the fivegroups G1-G5, one of which is illustrated in FIG. 6, is connected to thepositive terminal 104 via one of the lead wires 110, and to the negativeterminal 106 via the common wire 108. The control circuitry can beconfigured as part of the control system 1100 and can include circuits,control routines, controllers etc configured to vary one or more powerparameters used to drive ultrasound radiating members 40,

Referring now to FIG. 6, each group G1-G5 comprises a plurality ofultrasound radiating members 40. Each of the ultrasound radiatingmembers 40 is electrically connected to the common wire 108 and to thelead wire 310 via one of two positive contact wires 112. Thus, whenwired as illustrated, a constant voltage difference will be applied toeach ultrasound radiating member 40 in the group. Although the groupillustrated in FIG. 6 comprises twelve ultrasound radiating members 40,one of ordinary skill in the art will recognize that more or fewerultrasound radiating members 40 can be included in the group. Likewise,more or fewer than five groups can be included within the ultrasoundassembly 42 illustrated in FIG. 5.

FIG. 7A illustrates one preferred technique for arranging the componentsof the ultrasound assembly 42 (as schematically illustrated in FIG. 5)into the inner core 34 (as schematically illustrated in FIG. 4). FIG. 7Ais a cross-sectional view of the ultrasound assembly 42 taken withingroup G1 in FIG. 5, as indicated by the presence of four lead wires 110.For example, if a cross-sectional view of the ultrasound assembly 42 wastaken within group G4 in FIG. 5, only one lead wire 310 would be present(that is, the one lead wire connecting group G5).

Referring still to FIG. 7A, the common wire 108 comprises an elongate,flat piece of electrically conductive material in electrical contactwith a pair of ultrasound radiating members 40. Each of the ultrasoundradiating members 40 is also in electrical contact with a positivecontact wire 312. Because the common wire 108 is connected to thenegative terminal 106, and the positive contact wire 312 is connected tothe positive terminal 104, a voltage difference can be created acrosseach ultrasound radiating member 40. Lead wires 110 are preferablyseparated from the other components of the ultrasound assembly 42, thuspreventing interference with the operation of the ultrasound radiatingmembers 40 as described above. For example, in one preferred embodiment,the inner core 34 is filled with an insulating potting material 43, thusdeterring unwanted electrical contact between the various components ofthe ultrasound assembly 42.

FIGS. 7B and 7C illustrate cross sectional views of the inner core 34 ofFIG. 7A taken along lines 7B-7B and 7C-7C, respectively. As illustratedin FIG. 7B, the ultrasound radiating members 40 are mounted in pairsalong the common wire 108. The ultrasound radiating members 40 areconnected by positive contact wires 112, such that substantially thesame voltage is applied to each ultrasound radiating member 40. Asillustrated in FIG. 7C, the common wire 108 preferably comprises wideregions 108W upon which the ultrasound radiating members 40 can bemounted, thus reducing the likelihood that the paired ultrasoundradiating members 40 will short together. In certain embodiments,outside the wide regions 108W, the common wire 108 may have a moreconventional, rounded wire shape.

In a modified embodiment, such as illustrated in FIG. 7D, the commonwire 108 is twisted to form a helical shape before being fixed withinthe inner core 34. In such embodiments, the ultrasound radiating members40 are oriented in a plurality of radial directions, thus enhancing theradial uniformity of the resulting ultrasonic energy field.

One of ordinary skill in the art will recognize that the wiringarrangement described above can be modified to allow each group G1, G2,G3, G4, G5 to be independently powered. Specifically, by providing aseparate power source within the control system 100 for each group, eachgroup can be individually turned on or off, or can be driven with anindividualized power. This provides the advantage of allowing thedelivery of ultrasonic energy to be “turned off” in regions of thetreatment site where treatment is complete, thus preventing deleteriousor unnecessary ultrasonic energy to be applied to the patient.

The embodiments described above, and illustrated in FIGS. 5 through 7,illustrate a plurality of ultrasound radiating members groupedspatially. That is, in such embodiments, all of the ultrasound radiatingmembers within a certain group are positioned adjacent to each other,such that when a single group is activated, ultrasonic energy isdelivered at a specific length of the ultrasound assembly. However, inmodified embodiments, the ultrasound radiating members of a certaingroup may be spaced apart from each other, such that the ultrasoundradiating members within a certain group are not positioned adjacent toeach other. In such embodiments, when a single group is activated,ultrasonic energy can be delivered from a larger, spaced apart portionof the energy delivery section. Such modified embodiments may beadvantageous in applications wherein it is desired to deliver a lessfocused, more diffuse ultrasonic energy field to the treatment site.

In a preferred embodiment, the ultrasound radiating members 40 compriserectangular lead zirconate titanate (“PZT”) ultrasound transducers thathave dimensions of about 0.017 inches by about 0.010 inches by about0.080 inches. In other embodiments, other configuration may be used. Forexample, disc-shaped ultrasound radiating members 40 can be used inother embodiments. In a preferred embodiment, the common wire 108comprises copper, and is about 0.005 inches thick, although otherelectrically conductive materials and other dimensions can be used inother embodiments. Lead wires 110 are preferably 36 gauge electricalconductors, while positive contact wires 112 are preferably 42 gaugeelectrical conductors. However, one of ordinary skill in the art willrecognize that other wire gauges can be used in other embodiments.

As described above, suitable frequencies for the ultrasound radiatingmember 40 include, but are not limited to, from about 20 kHz to about 20MHz. In one embodiment, the frequency is between about 500 kHz and 20MHz, and in another embodiment 1 MHz and 3 MHz. In yet anotherembodiment, the ultrasound radiating members 40 are operated with afrequency of about 2 MHz.

FIG. 8 illustrates the inner core 34 positioned within the tubular body12. Details of the ultrasound assembly 42, provided in FIG. 7A, areomitted for clarity. As described above, the inner core 34 can be slidwithin the central lumen 51 of the tubular body 12, thereby allowing theinner core energy delivery section 41 to be positioned within thetubular body energy delivery section 18. For example, in a preferredembodiment, the materials comprising the inner core energy deliverysection 41, the tubular body energy delivery section 18, and the pottingmaterial 43 all comprise materials having a similar acoustic impedance,thereby minimizing ultrasonic energy losses across material interfaces.

FIG. 8 further illustrates placement of fluid delivery ports 58 withinthe tubular body energy delivery section 18. As illustrated, holes orslits are formed from the fluid delivery lumen 30 through the tubularbody 12, thereby permitting fluid flow from the fluid delivery lumen 30to the treatment site. Thus, a source of therapeutic compound coupled tothe inlet port 32 provides a hydraulic pressure which drives thetherapeutic compound through the fluid delivery lumens 30 and out thefluid delivery ports 58.

By evenly spacing the fluid delivery lumens 30 around the circumferenceof the tubular body 12, as illustrated in FIG. 8, a substantially evenflow of therapeutic compound around the circumference of the tubularbody 12 can be achieved. In addition, the size, location and geometry ofthe fluid delivery ports 58 can be selected to provide uniform fluidflow from the fluid delivery ports 30 to the treatment site. Forexample, in one embodiment, fluid delivery ports closer to the proximalregion of the energy delivery section 18 have smaller diameters thenfluid delivery closer to the distal region of the energy deliverysection 18, thereby allowing uniform delivery of fluid across the entireenergy delivery section.

For example, in one embodiment in which the fluid delivery ports 58 havesimilar sizes along the length of the tubular body 12, the fluiddelivery ports 58 have a diameter between about 0.0005 inches to about0.0050 inches. In another embodiment in which the size of the fluiddelivery ports 58 changes along the length of the tubular body 12, thefluid delivery ports 58 have a diameter between about 0.001 inches toabout 0.005 inches in the proximal region of the energy delivery section18, and between about 0.005 inches to 0.0020 inches in the distal regionof the energy delivery section 18. The increase in size between adjacentfluid delivery ports 58 depends on the material comprising the tubularbody 12, and on the size of the fluid delivery lumen 30. The fluiddelivery ports 58 can be created in the tubular body 12 by punching,drilling, burning or ablating (such as with a laser), or by any othersuitable method. Therapeutic compound flow along the length of thetubular body 12 can also be increased by increasing the density of thefluid delivery ports 58 toward the distal region 15 of the tubular body12.

It should be appreciated that it may be desirable to provide non-uniformfluid flow from the fluid delivery ports 58 to the treatment site. Insuch embodiment, the size, location and geometry of the fluid deliveryports 58 can be selected to provide such non-uniform fluid flow.

Referring still to FIG. 8, placement of the inner core 34 within thetubular body 12 further defines cooling fluid lumens 44. Cooling fluidlumens 44 are formed between an outer surface 39 of the inner core 34and an inner surface 16 of the tubular body 12. In certain embodiments,a cooling fluid can is introduced through the proximal access port 31such that cooling fluid flow is produced through cooling fluid lumens 44and out distal exit port 29 (see FIG. 1). The cooling fluid lumens 44are preferably evenly spaced around the circumference of the tubularbody 12 (that is, at approximately 120.degree. increments for athree-lumen configuration), thereby providing uniform cooling fluid flowover the inner core 34. Such a configuration is desirably to removeunwanted thermal energy at the treatment site. As will be explainedbelow, the flow rate of the cooling fluid and the power to theultrasound assembly 42 can be adjusted to maintain the temp of the innercore energy delivery section 41 within a desired range.

In a preferred embodiment, the inner core 34 can be rotated or movedwithin the tubular body 12. Specifically, movement of the inner core 34can be accomplished by maneuvering the proximal hub 37 while holding thebackend hub 33 stationary. The inner core outer body 35 is at leastpartially constructed from a material that provides enough structuralsupport to permit movement of the inner core 34 within the tubular body12 without kinking of the tubular body 12. Additionally, the inner coreouter body 35 preferably comprises a material having the ability totransmit torque. Suitable materials for the inner core outer body 35include, but are not limited to, polyimides, polyesters, polyurethanes,thermoplastic elastomers and braided polyimides.

In a preferred embodiment, the fluid delivery lumens 30 and the coolingfluid lumens 44 are open at the distal end of the tubular body 12,thereby allowing the therapeutic compound and the cooling fluid to passinto the patient's vasculature at the distal exit port. Or, if desired,the fluid delivery lumens 30 can be selectively occluded at the distalend of the tubular body 12, thereby providing additional hydraulicpressure to drive the therapeutic compound out of the fluid deliveryports 58. In either configuration, the inner core 34 can prevented frompassing through the distal exit port by making providing the inner core34 with a length that is less than the length of the tubular body. Inother embodiments, a protrusion is formed on the internal side of thetubular body in the distal region 15, thereby preventing the inner core34 from passing through the distal exit port.

In still other embodiments, the catheter 10 further comprises anocclusion device (not shown) positioned at the distal exit port 29. Theocclusion device preferably has a reduced inner diameter that canaccommodate a guidewire, but that is less than the inner diameter of thecentral lumen 51. Thus, the inner core 34 is prevented from extendingthrough the occlusion device and out the distal exit port 29. Forexample, suitable inner diameters for the occlusion device include, butare not limited to, about 0.005 inches to about 0.050 inches. In otherembodiments, the occlusion device has a closed end, thus preventingcooling fluid from leaving the catheter 10, and instead recirculating tothe proximal region 14 of the tubular body 12. These and other coolingfluid flow configurations permit the power provided to the ultrasoundassembly 42 to be increased in proportion to the cooling fluid flowrate. Additionally, certain cooling fluid flow configurations can reduceexposure of the patient's body to cooling fluids.

In certain embodiments, as illustrated in FIG. 8, the tubular body 12further comprises one or more temperature sensors 20, which arepreferably located within the energy delivery section 18. In suchembodiments, the proximal region 14 of the tubular body 12 includes atemperature sensor lead which can be incorporated into cable 45(illustrated in FIG. 1). Suitable temperature sensors include, but arenot limited to, temperature sensing diodes, thermistors, thermocouples,resistance temperature detectors (“RTDs”) and fiber optic temperaturesensors which use thermalchromic liquid crystals. Suitable temperaturesensor 20 geometries include, but are not limited to, a point, a patchor a stripe. The temperature sensors 20 can be positioned within one ormore of the fluid delivery lumens 30 (as illustrated), and/or within oneor more of the cooling fluid lumens 44.

FIG. 9 illustrates one embodiment for electrically connecting thetemperature sensors 20. In such embodiments, each temperature sensor 20is coupled to a common wire 61 and is associated with an individualreturn wire 62. Accordingly, n+1 wires can be used to independentlysense the temperature at n distinct temperature sensors 20. Thetemperature at a particular temperature sensor 20 can be determined byclosing a switch 64 to complete a circuit between that thermocouple'sindividual return wire 62 and the common wire 61. In embodiments whereinthe temperature sensors 20 comprise thermocouples, the temperature canbe calculated from the voltage in the circuit using, for example, asensing circuit 63, which can be located within the external controlcircuitry 100.

In other embodiments, each temperature sensor 20 is independently wired.In such embodiments, 2 n wires through the tubular body 12 toindependently sense the temperature at n independent temperature sensors20. In still other embodiments, the flexibility of the tubular body 12can be improved by using fiber optic based temperature sensors 20. Insuch embodiments, flexibility can be improved because only n fiber opticmembers are used to sense the temperature at n independent temperaturesensors 20.

FIG. 10 illustrates one embodiment of a feedback control system 68 thatcan be used with the catheter 10. The feedback control system 68 can beintegrated into the control system 1100 that is connected to the innercore 34 via cable 45 (as illustrated in FIG. 1). The feedback controlsystem 68 allows the temperature at each temperature sensor 20 to bemonitored and allows the output power of the energy source 70 to beadjusted accordingly. A physician can, if desired, override the closedor open loop system.

The feedback control system 68 preferably comprises an energy source 70,power circuits 72 and a power calculation device 74 that is coupled tothe ultrasound radiating members 40. A temperature measurement device 76is coupled to the temperature sensors 20 in the tubular body 12. Aprocessing unit 78 is coupled to the power calculation device 74, thepower circuits 72 and a user interface and display 80.

In operation, the temperature at each temperature sensor 20 isdetermined by the temperature measurement device 76. The processing unit78 receives each determined temperature from the temperature measurementdevice 76. The determined temperature can then be displayed to the userat the user interface and display 80.

The processing unit 78 comprises logic for generating a temperaturecontrol signal. The temperature control signal is proportional to thedifference between the measured temperature and a desired temperature.The desired temperature can be determined by the user (at set at theuser interface and display 80) or can be preset within the processingunit 78.

The temperature control signal is received by the power circuits 72. Thepower circuits 72 are preferably configured to adjust the power level,voltage, phase and/or current of the electrical energy supplied to theultrasound radiating members 40 from the energy source 70. For example,when the temperature control signal is above a particular level, thepower supplied to a particular group of ultrasound radiating members 40is preferably reduced in response to that temperature control signal.Similarly, when the temperature control signal is below a particularlevel, the power supplied to a particular group of ultrasound radiatingmembers 40 is preferably increased in response to that temperaturecontrol signal. After each power adjustment, the processing unit 78preferably monitors the temperature sensors 20 and produces anothertemperature control signal which is received by the power circuits 72.

The processing unit 78 preferably further comprises safety controllogic. The safety control logic detects when the temperature at atemperature sensor 20 has exceeded a safety threshold. The processingunit 78 can then provide a temperature control signal which causes thepower circuits 72 to stop the delivery of energy from the energy source70 to that particular group of ultrasound radiating members 40.

Because, in certain embodiments, the ultrasound radiating members 40 aremobile relative to the temperature sensors 20, it can be unclear whichgroup of ultrasound radiating members 40 should have a power, voltage,phase and/or current level adjustment. Consequently, each group ofultrasound radiating member 40 can be identically adjusted in certainembodiments. In a modified embodiment, the power, voltage, phase, and/orcurrent supplied to each group of ultrasound radiating members 40 isadjusted in response to the temperature sensor 20 which indicates thehighest temperature. Making voltage, phase and/or current adjustments inresponse to the temperature sensed by the temperature sensor 20indicating the highest temperature can reduce overheating of thetreatment site.

The processing unit 78 also receives a power signal from a powercalculation device 74. The power signal can be used to determine thepower being received by each group of ultrasound radiating members 40.The determined power can then be displayed to the user on the userinterface and display 80.

As described above, the feedback control system 68 can be configured tomaintain tissue adjacent to the energy delivery section 18 below adesired temperature. For example, it is generally desirable to preventtissue at a treatment site from increasing more than 6.degree. C. Asdescribed above, the ultrasound radiating members 40 can be electricallyconnected such that each group of ultrasound radiating members 40generates an independent output. In certain embodiments, the output fromthe power circuit maintains a selected energy for each group ofultrasound radiating members 40 for a selected length of time.

The processing unit 78 can comprise a digital or analog controller, suchas for example a computer with software. When the processing unit 78 isa computer it can include a central processing unit (“CPU”) coupledthrough a system bus. As is well known in the art, the user interfaceand display 80 can comprise a mouse, a keyboard, a disk drive, a displaymonitor, a nonvolatile memory system, or any another. Also preferablycoupled to the bus is a program memory and a data memory.

In lieu of the series of power adjustments described above, a profile ofthe power to be delivered to each group of ultrasound radiating members40 can be incorporated into the processing unit 78, such that a presetamount of ultrasonic energy to be delivered is pre-profiled. In suchembodiments, the power delivered to each group of ultrasound radiatingmembers 40 can then be adjusted according to the preset profiles.

The ultrasound radiating members are preferably operated in a pulsedmode. For example, in one embodiment, the time average electrical powersupplied to the ultrasound radiating members is between about 0.001watts and 5 watts and can be between about 0.05 watts and 3 watts. Incertain embodiments, the time average electrical power over treatmenttime is approximately 0.45 watts or 1.2 watts. The duty cycle is betweenabout 0.01% and 90% and can be between about 0.1% and 50%. In certainembodiments, the duty ratio is approximately 7.5%, 15% or a variationbetween 1% to 30%. The pulse averaged electrical power can be betweenabout 0.01 watts and 20 watts and can be between approximately 0.1 wattsand 20 watts. In certain embodiments, the pulse averaged electricalpower is approximately 4 watts, 8 watts, 16 watts, or a variation of 1to 8 watts. As will be described above, the amplitude, pulse width,pulse repetition frequency, average acoustic pressure or any combinationof these parameters can be constant or varied during each pulse or overa set of portions. In a non-linear application of acoustic parametersthe above ranges can change significantly. Accordingly, the overall timeaverage electrical power over treatment time may stay the same but notreal-time average power.

In one embodiment, the pulse repetition rate is preferably between about1 Hz and 2 kHz and more can be between about 1 Hz and 50 Hz. In certainpreferred embodiments, the pulse repetition rate is approximately 30 Hz,or a variation of 10 to 40 Hz. The pulse duration or width is can bebetween about 0.5 millisecond and 50 milliseconds and can be betweenabout 0.1 millisecond and 25 milliseconds. In certain embodiments, thepulse duration is approximately 2.5 milliseconds, 5 or a variation of 1to 8 milliseconds. In addition, the average acoustic pressure can bebetween about 0.1 to 2 MPa or in another embodiment between about 0.5 or0.74 to 1.7 MPa.

In one particular embodiment, the transducers are operated at an averagepower of approximately 0.6 watts, a duty cycle of approximately 7.5%, apulse repetition rate of 30 Hz, a pulse average electrical power ofapproximately 8 watts and a pulse duration of approximately 2.5milliseconds.

The ultrasound radiating member used with the electrical parametersdescribed herein preferably has an acoustic efficiency than 50% and canbe greater than 75%. The ultrasound radiating member can be formed avariety of shapes, such as, cylindrical (solid or hollow), flat, bar,triangular, and the like. The length of the ultrasound radiating memberis preferably between about 0.1 cm and about 0.5 cm. The thickness ordiameter of the ultrasound radiating members is preferably between about0.02 cm and about 0.2 cm.

With reference now to FIG. 11, the energy delivery section of anultrasound catheter that is configured for treating small vessels (e.g.,for treatment of cerebral vascular occlusions) is shown and thatincludes an optional cavitation promoting surface 71. In thisembodiment, the catheter includes an inner core 73 that defines autility lumen 72 configured to pass materials such as a guidewire, atherapeutic compound and/or a cooling fluid. The catheter assembly 70further includes a distal tip element 74 and a hollow cylindricalultrasound radiating member 77 that is mounted on the inner core 73.Certain of these components are optional, and are omitted fromalternative embodiments. In an example embodiment, the diameter of thecatheter outer body 76 is less than about 5 French, although otherdimensions are used in other embodiments. In addition, although only asingle ultrasound element is shown, in modified embodiments, more oneultrasound element can b mounted along the lumen 72.

In example embodiments, the ultrasound radiating member 77 illustratedin FIG. 11 s a tubular piezoceramic transducer that is able to radiateultrasonic energy in a length mode, a thickness mode, and acircumferential mode. The ultrasound radiating member 77 is capable ofgenerating a peak acoustic pressures that are preferably between about0.7 MPa and about 10 MPa, and that are more preferably between about 1.2MPa and about 6 MPa. However such parameters may be different if thecatheter includes cavitation promoting surfaces or other modifications.

In a modified embodiment, the ultrasound radiating member 77 has aresonant frequency greater than or equal to approximately 1 MHz in thethickness mode. In certain embodiments, the ultrasound radiating memberincluded in an ultrasound catheter optionally includes an electrode,such as a nickel-plated electrode, that enables electrical wires to besoldered thereto.

As will be described below, the ultrasound catheter includes one or moreone or more ultrasound radiating members positioned therein. Suchultrasound radiating members can comprise a transducer (e.g., a PZTtransducer), which is configured to convert electrically energy intoultrasonic energy. In such embodiments, the PZT transducer is excited byspecific electrical parameters (herein “power parameters” or “acousticparameters” that cause it to vibrate in a way that generates ultrasonicenergy). As will be explained below, Applicants have discovered thatnon-linearly varying (e.g., randomly or pseudo randomly) one or more ofthe power parameters the effectiveness of the ultrasound catheter (e.g.,the effectiveness of enhancing the removal of a thrombus) can besignificantly enhanced. By non-linearly varying one or more of the powerparameters the ultrasound radiating members create nonlinear acousticpressure, which as described above can increase the effectiveness of theacoustic pressure in enhancing a therapeutic compound. In oneapplication, the effect of nonlinearly varying acoustic pressure hasbeen found by Applicant to enhance enzyme medicated thrombolysis byalmost 1.9 times as compared to the application of substantiallyconstant acoustic pressure. Examples of nonlinear variances include, butare not limited to, multi variable variations, variations as a functionof a complex equation, sinusoidal variations, exponential variations,random variations, pseudo random variations and/or arbitrary variations.While nonlinear variance is preferred, in other arrangements it isanticipate that one or more of the parameters discussed can be varied ina linear manner either alone or combination with the nonlinear variance.

FIG. 12 will be used to explain certain power parameters which can usedto drive the ultrasound radiating members. As shown, the members can bedriven a series of pulses 2000 having peak power P or amplitude andduration T. During these pulses 2000, the ultrasound radiating membersas driven at a certain frequency f as described above by the electricalcurrent. The pulses 2000 can be separated by “off” periods 2100. Thecycle period T is defined as the time between pulse initiations, andthus the pulse repetition frequency (“PRF”) is given by T⁻¹. The dutycycle is defined as the ratio of time of one pulse to the time betweenpulse initiations TT⁻¹, and represents the fraction of time thatultrasonic energy is being delivered to the treatment site. The averagepower delivered in each cycle period is given by PTT⁻¹. Accordingly, theillustrated embodiment, the ultrasound radiating members are operatedusing pulses, or modulated electrical drive power instead of continuousdrive power

In one embodiment, the average power delivered in each cycle period ispreferably between about 0.1 watts and about 2.0 watts. In a such anembodiment, each cycle period has a different average power value,wherein the average power values for the different cycles vary in anonlinear fashion. Examples of non-linear variation include, but are notlimited to, simple or complex variable or multi-variable equations,varying randomly, pseudo randomly and/or in an arbitrary manner. Forinstance, in one such modified embodiment, each cycle period has anaverage power quantity that is randomly or pseudo randomly distributedbetween a maximum average power quantity and a minimum average powerquantity. The average power of each cycle period can be adjusted bymanipulating one or more parameters of the waveform in the cycle period,such as, but not limited to, peak power P, reduced power P′, pulserepetition frequency, pulse duration T, and duty cycle.

In another embodiment, the duty cycle is preferably between about 1% andabout 50%, is more preferably between about 2% and about 28%. Duringoperation of the catheter, the duty cycle can vary in a nonlinearfashion. For instance, in one such modified embodiment, the duty cyclethat is randomly or pseudo randomly distributed between a maximum dutycycle and a minimum duty cycle. For example, in one embodiment, thevalues for the maximum duty cycle are between about 25% and about 30%,and typical values for the minimum duty cycle are between about 1.5% andabout 3.5%. In yet another embodiment, the duty cycle is variednon-linearly from a minimum value of 2.3% and a maximum value of 27.3%.In one embodiment, other parameters of the waveform are manipulated suchthat each cycle period has the same average power, even though the dutycycle for each cycle period is varying in a nonlinear fashion.

In another embodiment, the peak power P delivered to the treatment siteis preferably between about 0.1 watts and about 20 watts, is morepreferably between about 5 watts and about 20 watts, and is mostpreferably between about 8 watts and about 16 watts. Within the ranges,during operation of the catheter, the peak power P can vary in anonlinear fashion. For instance, in one such modified embodiment, eachcycle period has a peak power quantity that is randomly or pseudorandomly distributed between a maximum peak power P_(max) and a minimumpeak power P_(min). Typical values for the maximum peak power P_(max)are between about 6.8 watts and about 8.8 watts, and typical values forthe minimum peak power P_(min) are between about 0.1 watts and about 1.0watts. In another embodiment, the peak power is varied non-linearlybetween a maximum peak power P_(max) of 7.8 watts and a minimum peakpower P_(min) of 0.5 watts. In one embodiment, other parameters of thewaveform are manipulated such that each cycle period has the sameaverage power, even though the peak power P for each cycle period isvarying in a nonlinear fashion.

In another embodiment, the effect of a therapeutic compound isoptionally enhanced by using a certain pulse repetition frequency PRFand/or a certain pulse duration T. In one example embodiment, the PRF ispreferably between about 5 Hz and about 150 Hz, is more preferablybetween about 10 Hz and about 50 Hz, and is most preferably betweenabout 20 Hz and about 40 Hz. In one embodiment, the PRF remainssubstantially constant during the course of a treatment. However, incertain modified embodiments the PRF is non-linearly varied during thecourse of a treatment within the ranges described above. For example, inone such modified embodiment the PRF is varied linearly during thecourse of the treatment, while in another such modified embodiment thePRF is varied nonlinearly during the course of the treatment. Examplesof nonlinear variances include, but are not limited to, sinusoidalvariations, exponential variations, and random variations. For instance,in an example embodiment the PRF is varied randomly between a maximumPRF and a minimum PRF during the course of a treatment. Typical valuesfor the maximum PRF are between about 28 Hz and about 48 Hz, and typicalvalues for the minimum PRF are between about 5 Hz and about 15 Hz. Inanother embodiment, the maximum PRF is about 38 Hz and the minimum isabout 10 Hz. In one embodiment, the pulse repetition interval is variedbetween about 25 to about 100 ms.

The pulse amplitude, pulse width and pulse repetition frequency duringeach pulse can also be constant or varied in a non-linear fashion asdescribed herein. Other parameters are used in other embodimentsdepending on the particular application.

In one example embodiment, the pulse duration T is preferably betweenabout 1 millisecond and about 50 milliseconds, is more preferablybetween about 1 millisecond and about 25 milliseconds, and is mostpreferably between about 2.5 milliseconds and about 5 milliseconds. In amodified embodiment, each cycle period has a different pulse duration T,wherein the pulse duration values vary in a nonlinear fashion with theranges described above. For instance, in one such modified embodiment,each cycle period has a pulse duration quantity that is randomlydistributed between a maximum pulse duration T _(max) and a minimumpulse duration T _(min). Typical values for the maximum pulse duration T_(max) are between about 6 milliseconds and about 10 milliseconds (andin one embodiment 8 milliseconds), and typical values for the minimumpulse duration T _(min) are between about 0.1 milliseconds and about 2.0milliseconds (and in one embodiment 1 millisecond), In one embodiment,other parameters of the waveform are manipulated such that each cycleperiod has the same average power, even though the pulse duration T foreach cycle period is varying in a nonlinear fashion. In otherembodiments, the average power can be varied non-linearly.

In addition, the average acoustic pressure can also non-linearly variedas described above between about 0.1 to 2 MPa or in another embodimentbetween about 0.5 or 0.74 to 1.7 MPa.

The control system 1100 can be configured to vary one or more of thepower parameters as discussed above. Accordingly, the control system1100 can include any of a variety of control routines, control circuits,etc. so as to vary the power parameters described above. As mentionedabove, the control parameters can be varied in combination with otheroperating parameters (e.g., frequency) of the ultrasound radiatingmember and/or catheter. Alternatively, the power parameters may bevaried using a software package that controls the operation of theultrasound radiating members. It should also be appreciated that one,two, three or all of the parameters (and subsets thereof) can benon-linearly varied at the same time or by themselves.

A study to investigate the effect of a variety of randomizationprotocols on clot lysis was conducted. The randomization protocolsinvolved non-linearly varying peak power, pulse width, pulse repetitionfrequency, or combinations of the above. The randomization protocolswere tested using a time average power of either 0.45 W or 0.90 W, andwere compared to a standard Neurowave E11 protocol.

Clots were prepared by adding 1 mL of citrated human pooled plasma to apolystyrene culture tube. Clotting was initiated by the addition of 100μL of 0.2 M calcium chloride and 100 μL of 12.5 U/ml bovine thrombin.Fixtures equipped with drug delivery lumens and an ultrasonic catheterwere inserted into the clot, thereby allowing the clot to form aroundthe fixtures. Clots were allowed to incubate for 10 minutes in a 37degrees C. water bath before initiating the clot lysis procedure.

Clot lysis was initiated by delivering rt-PA to the clot via the drugdelivery lumens. A total of 0.08 mL of 5000 U/mL rt-PA solution wasdelivered to the clot over a period of 5 minutes at a rate of 0.96mL/hr.

After drug delivery was completed, the clot was subjected to 5 minutesof ultrasound exposure, and 25 minutes of additional incubation timesubsequent to the ultrasound treatment. The clots were then removed fromthe polystyrene culture tubes and pressed between filter paper to removeserum from the clots before the clots were weighed.

The acoustic protocols tested are summarized in Table 1 provided below.“PW” represents pulse width and “PRF” represents pulse repetitionfrequency. Ranges indicate that the parameter was varied randomly withinthe range shown. For example, for the R3P-d protocol, peak power wasvaried from 1.6 to 7.9 W, pulse width was varied from 1.16 to 8.16 ms,and pulse repetition frequency was varied from 10 to 40 Hz.

TABLE 1 Description of acoustic protocols Average Peak Acoustic ProtocolPower Power PW PRF Neurowave E11 0.45 W    5.3 W     2.8 ms 30 Hz(E11-S) R3P-d (R1.4) 0.45 W 1.6-7.9 W 1.16-8.16 ms 10-40 Hz   R1P-f(R5.5) 0.45 W    3.75 W 0.31-19.53 ms  30 Hz R1P-g (R5.6) 0.90 W    3.75W 0.62-39.07 ms  30 Hz R2P-a (R6.0) 0.45 W 1.6-7.9 W  0.54-9.8 ms 30 HzR2P-b (R6.1) 0.90 W 1.6-7.9 W 1.09-19.6 ms 30 Hz

The randomization protocols were compared to the fixed parameterNeurowave E11 protocol as described in Table 1. Lysis enhancement factor(LEF %) was calculated using the following formula:

${{LEF}\mspace{11mu} \%} = {\left( {\left( \frac{W_{c} - W_{{lus}_{i}}}{W_{c} - W_{l}} \right) - 1} \right) \times 100}$

The variables in the above equation are:W_(c)[mg]: Average clot weight of the negative control samples (notreatment).W_(l)[mg]: Average clot weight from positive control group (drugtreatment only).W_(lus)[mg]: Average clot weight from each individual ultrasoundtreatment group.

FIG. 13 shows the LEF % for the protocols tested. The results indicatethat varying peak power and pulse width simultaneously in therandomization protocol give significantly better lysis enhancement inthe test environment than varying either parameter alone or when theyare varied together with pulse repetition frequency. In addition, higherpeak powers generally yielded improved lysis response. It should beappreciated that the Lysis enhancement factor is only one measure of theefficacy of the treatment and that the methods and technique describedabove may have additional and/or different efficacy benefits in situ.

In one embodiment, one way of implementing a randomization protocol isto generate and execute a plurality of ultrasonic cycle profiles, whereeach ultrasonic cycle profile can have randomly generated powerparameter values. As previously mentioned, power parameters include, butare not limited to, peak power, pulse width, pulse repetition frequencyand pulse repetition interval. Generally, for each power parameter, arandom number generator, for example, can be used to select a valuewithin a bounded range determined by the operator. Examples of suitableranges are described above. For example, one ultrasonic cycle profilecan have a randomly selected peak power value, while the other powerparameters are non-randomly selected. Another ultrasonic cycle profilemay have a plurality of randomly selected power parameters values, suchas peak power and pulse width. This process can be used to generate thedesired number of ultrasonic cycle profiles.

Each ultrasonic cycle profile can be run for a profile execution time.For example, if the profile execution time is approximately 5 seconds,each ultrasonic cycle profile will be run for approximately 5 secondsbefore the next ultrasonic cycle profile is run. In some embodiments,the profile execution time is less than about 5 seconds. For example, insome embodiments the profile execution time is between about one secondand about 30 seconds. In some embodiments, the profile execution time isless than about one second. In some embodiments, the profile executiontime is increased so that accurate measurements can be taken of theexecuted power parameters. In some embodiments, the profile executiontime itself can be selected randomly from a predetermined range.

In some embodiments, it is desirable to deliver a particular timeaveraged power. Because the power parameters may be randomized, it maytake the execution of a plurality of ultrasonic cycle profiles beforethe time averaged power approaches an asymptotic value. In someembodiments, the execution of about 40 to 50 ultrasonic cycle profilesis required for the time averaged power to become asymptotic. In otherembodiments, less than about 40 ultrasonic cycle profiles are required,while in yet other embodiments, more than about 50 ultrasonic cycleprofiles are required. In some embodiments, ultrasonic cycle profilesare executed until the time average power approaches an asymptoticvalue. For example, if the profile execution time is 5 seconds and theoverall execution time is 30 minutes, 360 ultrasonic cycle profiles willbe executed, which in some embodiments is sufficient for the timeaverage power to approach an asymptotic value.

In addition, although many embodiments have been described in thecontext of an intravascular catheter it should be appreciated that thenon-linear application of one or more power parameters can also beapplied to non-intravascular catheters or devices and/or non catheterapplications. For example, the non-linear varying of one or more powerparameters may also find utility in applications in which the ultrasoundis applied through an external (with respect to the body or with respectto the vascular system). In particular, the discussion above can beapplied to external ultrasound application in which the ultrasoundsource is external to the patient and/or treatment site. It is alsoanticipated that the methods and techniques described herein can beapplied to non-vascular applications. In addition, in some embodiments,the therapeutic affects of the ultrasound can be utilized alone withouta therapeutic compound.

SCOPE OF THE INVENTION

While the foregoing detailed description discloses several embodimentsof the present invention, it should be understood that this disclosureis illustrative only and is not limiting of the present invention. Itshould be appreciated that the specific configurations and operationsdisclosed can differ from those described above, and that the methodsdescribed herein can be used in contexts other than treatment ofvascular occlusions.

1. An ultrasound catheter system comprising: a catheter having at leastone ultrasonic element; a control system configured to generate powerparameters that drive the at least one ultrasonic element to generateultrasonic energy; wherein the control system is configured to varynon-linearly at least one of the power parameters.
 2. The system ofclaim 1, wherein the power parameters comprise at least one of peakpower, pulse repetition frequency, pulse width or any combination ofaforementioned parameters.
 3. The system of claim 1, wherein the atleast one acoustic parameter is varied randomly between a maximum valueand a minimum value.
 4. A method of operating an ultrasonic cathetercomprising: advancing a catheter with at least one ultrasonic element toa treatment site in a patient's vascular system; driving the at leastone ultrasonic element to generate ultrasonic energy; delivering atherapeutic compound to the treatment site through the catheter; andnon-linearly varying a power parameter of the ultrasonic element.
 5. Themethod of claim 4, wherein the power parameter comprises at least one ofpeak power, pulse repetition frequency, pulse width and duty cycle. 6.The method of claim 1, wherein the power parameter is varied randomlybetween a maximum value and a minimum value.
 7. The method of claim 4,wherein the treatment site includes a vascular occlusion.
 8. The methodof claim 4, wherein the therapeutic compound comprises a thrombolyticagent.
 9. A control system for an ultrasound catheter comprising acontrol unit configured to non-linearly vary a power parameter of anultrasonic element of an ultrasonic catheter.
 10. The system of claim 9,wherein the power parameter comprises at least one of peak power, pulserepetition frequency, pulse width and duty cycle.
 11. The system ofclaim 9, wherein the power parameter is configured to be varied randomlybetween a maximum value and a minimum value.
 12. An ultrasoundtherapeutic system comprising: an ultrasonic delivery device having atleast one ultrasonic element; and a control system configured togenerate power parameters that drive the at least one ultrasonic elementto generate ultrasonic energy; wherein the control system is configuredto vary non-linearly at least one of the power parameters.
 13. Thesystem of claim 12, wherein the power parameters comprise at least oneof peak power, pulse repetition frequency, pulse width and duty cycle.14. The system of claim 12, wherein the at least one power parameter isvaried randomly between a maximum value and a minimum value.
 15. Amethod of delivering ultrasound to a patient comprising: advancing acatheter with at least one ultrasonic element to a treatment site in apatient's vascular system; driving the at least one ultrasonic elementto generate ultrasonic energy; and non-linearly varying a powerparameter of the ultrasonic element.
 16. The method of claim 15, whereinthe power parameter comprises at least one of peak power, pulserepetition frequency, pulse width and duty cycle.
 17. The method ofclaim 15, wherein the power parameter is varied randomly between amaximum value and a minimum value.
 18. The method of claim 15, furthercomprising delivering a therapeutic compound to the patient.